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Aspirant
Posts: 2
Registered: ‎2012-07-03

Changing Router IP Address

Hi everyone, I am trying to change my routers public IP address.

If I connect directly to my modem and power cycle it, I can get a new address. But, if I connect the modem back to the router and power cycle it - no matter what I do I get the exact same IP address. In the router settings I have "Get Dynamically from ISP" checked. I'm not concerned with the IP address of my individual computer, as that is not a problem. But I am unable to connect directly to my modem with my laptop, so I am stuck with the address that my WNDR3700 keeps using.

My question is why it continues to pull up the same IP address. I've tried changing it statically and power cycling it, just in hopes that when I change it back to Dynamic it will get a new address. At the very bottom of the page it says "Use default MAC address" and that is checked. If the public router IP is related to the MAC address, will changing that to "Use computers MAC Address" change the public IP?

I've tried contacting Comcast (my ISP) who wanted $80 to remotely connect to my computer, and Netgear who also informed me I'm outside of their warranty. There has to be SOME way to change my routers public IP, please help!

P.S. I'm a computer science major, so I'm not clueless. If anyone has steps, just please provide them to me. Thanks!

.t2h
Aspirant
Posts: 21
Registered: ‎2011-11-19

Re: Changing Router IP Address

It's not quite clear from your post why it is important that you get a different IP on the router. Also, it is not quite clear if the addresses you are getting are private or public IPs.

Generally, if the ISP is uisng DHCP, DHCP will hold the IP address for the client's unique MAC address (PC attached to modem or Router attached to modem) until the lease expires. You can see the 'lease expires' period when you have the modem attached to a PC/laptop running Windows with the ipconfig /all command. If the MAC address facing the modem changes, and the ISP's DHCP server does not already have lease for that MAC then a new one may be assigned.

This is a moot point if your modem is in fact a router and offering up public IP addresses. I don't like such configurations as they often result in double-NAT and the issues tha come with it - so I configure my modem for pass-through.
Luminary
Posts: 89,285
Registered: ‎2009-01-27

Re: Changing Router IP Address

if I connect the modem back to the router and power cycle it - no matter what I do I get the exact same IP address. I


This is normal for cable modem. ISP will NOT renew the IP for longer duration so you will NOT able to change WAN IP at your will.

Only way to do that is to use Mac Spoof but you will run out of mac address to keep changing.

You will be wasting time on this matter specially comcast will keep same IP to it's mac address for minim 30days or plus
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June Mizoguchi-
Aspirant
Posts: 2
Registered: ‎2012-07-03

Re: Changing Router IP Address

To the first poster, I said my public IP address. I did not mention why I wanted to change my IP address as it is irrelevant.

To the second poster, I think that answers my question and explains why I can get a different IP for my devices but the router is specific.

Is there a method to changing MAC addresses?
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Luminary
Posts: 89,285
Registered: ‎2009-01-27

Re: Changing Router IP Address

"Use computers MAC Address"


Like said, you will RUN OUT of mac address to do this. Most people keep asking about this issue are commonly block from forum that blocks it's IP etc.

You can not just magically come up with mac address for NIC, Each NIC has unique mac address assigned so if you have 4 PC then you can alternative change router to use it's mac address but if comcast will keep each duration for X amount of time/duration then you will some point will NOT able to get new ip address or depending on how cycle will work for you
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June Mizoguchi-
Aspirant
Posts: 21
Registered: ‎2011-11-19

Re: Changing Router IP Address

Fair enough, .t2h, you did say 'public IP' and I simply assumed by that you meant it was simply whatever was assigned to the device interface facing your modem - wethor the address was from a sanctioned public block or a private block - as either can be assigned to the external interface of the router depending upon wethor or not passthrough is used by the modem. My apologies if this came as anything else to you. Also, in my post, 3rd paragraph, I meant to say, "private IP". Unfortuantely, it was a long morning without coffee for me.

I asked about 'Why' you would need to do this because I have a duty, as a Certified Information Systems Security Professional, to protect the infrastructure. Rapidly changing your MAC address may cause a denial of service to you and other consumers and is not normal operation.

If I understood your ultimate goals I might be able to suggest a more approropriate workaround.
Tutor
Posts: 2,017
Registered: ‎2010-02-22

Re: Changing Router IP Address

Actually you can just make up a MAC as you wish.

I doubt any ISP's filter by the registering MAC.

Router web page.
"Basic Settings"
"Use this Mac Address"
Type in whatever you want. I would avoid 00 or FF as the first two digits.
You only need change the last two digits. After you do it then you may need to power cycle your modem.
Luminary
Posts: 89,285
Registered: ‎2009-01-27

Re: Changing Router IP Address

Actually you can just make up a MAC as you wish.

True.. I was going to say too but I like to keep it basic in order complicate the issue and use wisely

Smiley Happy
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June Mizoguchi-
Prodigy
Posts: 8,425
Registered: ‎2006-11-24

Re: Changing Router IP Address

I have a question for you guys, and feel free not to answer it

Can I use ABCDEFGHIJKLMNOPQRSTUVWXYZ as my MAC address?
Can I put - youransweriswrong - as my MAC address?

The simple truth is neither of the above examples will work, so you can't actually make up a MAC as you wish, there are rules that must be followed, and reasons those rules exist - yes, if you know the basic rules you can create a completely ficticious MAC address, but you do so at your own risk.

There's a time and a place to use MAC spoofing, and there are reasons why it should not be done.

Give a man a fish, feed him for a day
Teach a man to fish, feed him for life.
Luminary
Posts: 89,285
Registered: ‎2009-01-27

Re: Changing Router IP Address

Can I use ABCDEFGHIJKLMNOPQRSTUVWXYZ as my MAC address?
Can I put - youransweriswrong - as my MAC address?


funny man... figure rest new the what mac address should be.. Smiley Happy
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June Mizoguchi-
Aspirant
Posts: 21
Registered: ‎2011-11-19

Re: Changing Router IP Address

fordem wrote:

There's a time and a place to use MAC spoofing, and there are reasons why it should not be done.


Very agreed.

Although MAC spoofing is a legitimate feature of networking devices, and indeed, required in some circumstances (and IMHO not complicated at all), there are other circumstances in which it is not a good solution
....Much like, although it is possible to drive a car to the ocean and into it, most cars are not meant for water and as such, it is not a good solution to drive one across the big ponds yet a boat will suffice well...

Sometimes we simply need to select more suitable equipment for the job.
Tutor
Posts: 2,017
Registered: ‎2010-02-22

Re: Changing Router IP Address

fordem wrote:
I have a question for you guys, and feel free not to answer it

Can I use ABCDEFGHIJKLMNOPQRSTUVWXYZ as my MAC address?
Can I put - youransweriswrong - as my MAC address?

The simple truth is neither of the above examples will work, so you can't actually make up a MAC as you wish, there are rules that must be followed, and reasons those rules exist - yes, if you know the basic rules you can create a completely ficticious MAC address, but you do so at your own risk.

There's a time and a place to use MAC spoofing, and there are reasons why it should not be done.


Your overcomplicating the answer.
But if my "You can use any" was not specific enough then i guess I can clear it up.

You can use 6 groups of two hexadecimal digits ranging between but not including 00:00:00:00:00:00 to FF:FF:FF:FF:FF.FF

From a "my isp ties MAC to IP" I can see no reason why it should not be done, but I am open to suggestions.

My responce was mainly to go against the reply saying that you would run out of MAC's.
Aspirant
Posts: 21
Registered: ‎2011-11-19

Re: Changing Router IP Address

jlewter wrote:
My responce was mainly to go against the reply saying that you would run out of MAC's.


If a device that aquires its IP address from a DHCP server changes MAC addreses, the DHCP server will track it as a different device and issue a different address from the available DHCP pool. If that device rapidly changes it's MAC address over-and-over, such as someone trying get around an IP address based exclusion rule might try to script, it is quite possible for the device to request enough addresses to exhaust the DHCP server's pool of available. In such a case, subequent attempts to use a new MAC address will fail to be aquire an address from the DHCP server - and be useless --- unless the goal is to cause a Denial of Service attack on the DHCP server.

So yes, it is unlikely you could change your MAC often and fast enough to try every possible MAC in the MAC-48 scheme. If you could, you would definately conflict with another device in the colision domain. But, odds are, you would run into a DHCP pool exaustion senario first.
Tutor
Posts: 2,017
Registered: ‎2010-02-22

Re: Changing Router IP Address

CableCo's usually limit the number of IP changes over a given time per customer (based on the Modem MAC) to avoid users flooding the service. If a user does flood a service then It's quite likely that the user will be looking for a new ISP within a month or so Smiley Happy.

There are scripts that do this, It's to get around those "Free" servers that offer game demo's and such. Quite often they only give the first (x) number of downloads a month free at full speed, then the rest is restricted.

It is also worth noting that if two users use the same MAC on their router, on the same ISP, the ISP will still know who each customer is based on the IP (Modem's ISP Private Side) that the request has came from. If two users are on the same node then it is possible that there could be a ip/routing conflict.

Some users want to change IP's because they think it gets them around piracy monitoring, this is wrong and it just doesnt work that way. The main reason is what I said above, and other than that it comes down to getting around things like forum/game/IRC/newsgroup bans based on IP.
Aspirant
Posts: 78
Registered: ‎2011-11-05

Re: Changing Router IP Address

Alnico wrote:
Fair enough, .t2h, you did say 'public IP' and I simply assumed by that you meant it was simply whatever was assigned to the device interface facing your modem - wethor the address was from a sanctioned public block or a private block - as either can be assigned to the external interface of the router depending upon wethor or not passthrough is used by the modem. My apologies if this came as anything else to you. Also, in my post, 3rd paragraph, I meant to say, "private IP". Unfortuantely, it was a long morning without coffee for me.

I asked about 'Why' you would need to do this because I have a duty, as a Certified Information Systems Security Professional, to protect the infrastructure. Rapidly changing your MAC address may cause a denial of service to you and other consumers and is not normal operation.

If I understood your ultimate goals I might be able to suggest a more approropriate workaround.


I'm also a CISSP, but I'm not sure why the OP needs to change his public IP, that is, the one that Comcast uses to route to his home network.

That all said, I went away on a trip in June for about 10 days, so I powered down as much as I could around the house, set-top boxes, printers, router, etc. When I powered up again, I found that my router's public IP address had changed.

Is 10 days enough? YMMV. Smiley Happy And who wants to be off the grid for 10 days anyway? Smiley Very Happy
Home LAN includes 2 Win 7 desktops, 2 Win 7 laptops, 2 iPads, 2 iPhones, 1 "smart" TV. ISP is Comcast.
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